The fact that lemmy.world is the size of the rest of the large Lemmy instances combined can be useful if you are starting a community because there are a lot of local users who will just spot your community from “Local” and you can get thousands of more followers. It’s also run by a well-known and well-founded non-profit so they have the knowhow and finance to pretty much guarantee that they are going to stick around.

However, as people have found, it can slow down. As they run mastodon.world and calckey.world and Reddit and Twitter both threw spanners in their own works last weekend they were likely scrambling to boost capacity and it showed the strain. There are also concerns about everything being centralised in just a few big instances on each service. I don’t see a way the .world instances could be taken over by commercial interests so I think we’re alright from that front but we can’t predict the future.